Use the attached project to reproduce.

Workaround:
private void RadForm1_SizeChanged(object sender, EventArgs e)
{
    if (this.WindowState == FormWindowState.Normal)
    {
        this.SizeChanged -= RadForm1_SizeChanged;
        this.Size = new Size(this.Size.Width + 1, this.Size.Height + 1);
        this.Size = new Size(this.Size.Width - 1, this.Size.Height - 1);

        this.SizeChanged += RadForm1_SizeChanged;
    }
}

To reproduce:

1. Collapse the ribbon
2. Select the tab to show the popup
3. Type some text in the RadDropDownListElement
4. Press Escape, Enter, Backspace keys. You will notice that these keys are not handled by the drop down. However, the ribbon popup is closed and there is no way to handle these keys.

Set the RadGalleryElement.DropDownSizingMode property to Telerik.WinControls.UI.SizingMode.None. however, you will notice that when the gallery's popup is opened, the grip is visible. Please refer to the attached project.

Workaround:

Sub New()
    
    InitializeComponent()

    AddHandler Me.RadGalleryElement1.DropDownOpened, AddressOf DropDownOpened

End Sub

Private Sub DropDownOpened(sender As Object, e As EventArgs)
    Me.RadGalleryElement1.GalleryPopupElement.SizingGrip.SizingMode = Telerik.WinControls.UI.SizingMode.None
End Sub

How to reproduce: the issue is only reproducible in client`s environment, Windows 10 build 1607
Public Class Form1

    Sub New()
        InitializeComponent()

    End Sub

    Protected Overrides Sub OnLoad(e As EventArgs)
        MyBase.OnLoad(e)

        Me.RadGalleryElement1.MaxRows = 1

        For i As Integer = 0 To 149
            Dim blueItem1 As New RadGalleryItem("", My.Resources.RibbonBar_GettingStarted_CreatingAGallery001)
            Me.RadGalleryElement1.Items.Add(blueItem1)
        Next
    End Sub

End Class

Workaround: 
Public Class Form1

    Sub New()
        InitializeComponent()

        AddHandler Me.RadGalleryElement1.DropDownOpening, AddressOf RadGalleryElement1_DropDownOpening

    End Sub

    Protected Overrides Sub OnLoad(e As EventArgs)
        MyBase.OnLoad(e)

        Me.RadGalleryElement1.MaxRows = 1

        For i As Integer = 0 To 149
            Dim blueItem1 As New RadGalleryItem("", My.Resources.RibbonBar_GettingStarted_CreatingAGallery001)
            Me.RadGalleryElement1.Items.Add(blueItem1)
        Next
    End Sub

    Private Sub RadGalleryElement1_DropDownOpening(sender As Object, e As System.ComponentModel.CancelEventArgs)
        Dim gallery = DirectCast(sender, RadGalleryElement)
        Dim popup = gallery.GalleryDropDown.PopupElement
        Dim wa = Screen.PrimaryScreen
        popup.Children(0).MaxSize = New Size(0, wa.Bounds.Height)

    End Sub

End Class

To reproduce:
- Add complex controls to the backstage pages (add at least 4 pages).
- Change the pages at runtime.

Workaround:
Private Sub RadRibbonBarBackstageView1_BackstageViewOpening(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles RadRibbonBarBackstageView1.BackstageViewOpening
    BackstageViewPage1.Visible = True
    BackstageViewPage2.Visible = True
    BackstageViewPage3.Visible = True
    BackstageViewPage4.Visible = True
End Sub

The issue can be reproduced after creating ribbon groups with buttons having large pictures and TextImageRelation set to ImageAboveText

Workaround: handle the DropDownOpened event of the buttons and set a MaxSize to the ElementWithCaptionLayoutPanel child
public Form1()
{
    InitializeComponent();

    //Workaround
    this.radRibbonBarGroup1.DropDownElement.DropDownOpened += DropDownElement_DropDownOpened;
    this.radRibbonBarGroup2.DropDownElement.DropDownOpened += DropDownElement_DropDownOpened;
    this.radRibbonBarGroup3.DropDownElement.DropDownOpened += DropDownElement_DropDownOpened;
}

private void DropDownElement_DropDownOpened(object sender, EventArgs e)
{
    RadRibbonBarGroupDropDownButtonElement element = (RadRibbonBarGroupDropDownButtonElement)sender;
    RadRibbonBarGroupDropDownMenuElement menuElement = (RadRibbonBarGroupDropDownMenuElement)element.DropDownMenu.PopupElement;
    ElementWithCaptionLayoutPanel layoutPanel = menuElement.Layout.FindDescendant<ElementWithCaptionLayoutPanel>();
    menuElement.Layout.FindDescendant<ElementWithCaptionLayoutPanel>().MaxSize = new Size(0, 77);
}

How to reproduce: just create a ribbon form with many collapsed ribbon bar groups, e.g. 20 and try to resize the form:

Workaround: change all RadRibbonBarGrpoup instances with the custom class below
public class MyRadRibbonBarGroup : RadRibbonBarGroup
{
    override public bool ExpandElementToStep(int collapseStep)
    {
        bool result = false;
        if (!this.CanCollapseOrExpandElement(ChunkVisibilityState.Expanded))
        {
            return result;
        }

        this.InvalidateIfNeeded();

        if (this.CollapseStep == (int)ChunkVisibilityState.Collapsed)
        {
            this.ExpandChunkFromDropDown();
            --this.CollapseStep;
            result = true;
            this.CollapseCollection((int)ChunkVisibilityState.NoText);
        }
        else
        {
            result = this.ExpandCollection(collapseStep);
        }

        return result;
    }

    private void ExpandChunkFromDropDown()
    {
        this.DropDownElement.Visibility = ElementVisibility.Collapsed;
        this.DropDownElement.Items.Clear();

        ElementWithCaptionLayoutPanel el = (ElementWithCaptionLayoutPanel)typeof(RadRibbonBarGroup).GetField("elementWithCaptionLayoutPanel", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(this);

        this.Children.Add(el);
    }

    private bool CanCollapseOrExpandElement(ChunkVisibilityState state)
    {
        if (this.IsDesignMode)
        {
            return false;
        }

        return true;
    }
}

To reproduce:

LightVisualElement caption = new LightVisualElement();
caption.MinSize = new Size(150, 20);
caption.DrawText = true;
caption.DrawImage = true;
caption.TextImageRelation = TextImageRelation.ImageBeforeText;
caption.Text = "My Application";
caption.Image = Image.FromFile(@"..\..\delete.png");
caption.ShouldHandleMouseInput = false;
caption.NotifyParentOnMouseInput = true;
caption.ImageLayout = ImageLayout.None;
caption.ImageAlignment = ContentAlignment.TopLeft;
caption.TextAlignment = ContentAlignment.TopLeft;
this.radRibbonBar1.RibbonBarElement.RibbonCaption.CaptionLayout.Children.Add(caption);

Use attached project to reproduce.

Workaround
radRibbonBar1.StartMenuItems.RemoveAt(0);

To reproduce: click the application menu drop down to open the backstage view. Then, click the button again to close it. You will notice that the BackstageViewClosing/BackstageViewClosed events are fired twice

How to reproduce:  subcribe to the Click event handled of a RadSplitButtonElement added to a certain group in RadRibbonBar, notice that when you click on the button the event will fire two times

Workaround: 
bool cancel;
private void radSplitButtonElement1_Click(object sender, EventArgs e)
{
    if (!cancel)
    {
        //Handle Click event;
        this.cancel = true;
        return;
    }

    this.cancel = false;
}

To reproduce: please run the attached sample project and follow the steps from the gif file.

Workaround: close the popup before showing the message or the dialog:


        private void radButtonElement1_Click(object sender, EventArgs e)
        {
              if (!radRibbonBar1.Expanded)
            {
                this.radRibbonBar1.RibbonBarElement.Popup.ClosePopup(Telerik.WinControls.UI.RadPopupCloseReason.Mouse);
            }
            RadMessageBox.Show("Test");
        }

Workaround: this.radDropDownButtonElement1.ActionButton.TextElement.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAliasGridFit; 

To reproduce: please refer to the attached sample project and gif file.

Workaround:  this.radRibbonBar1.RibbonBarElement.ApplicationButtonElement.DropDownOpened+=ApplicationButtonElement_DropDownOpened;

 private void ApplicationButtonElement_DropDownOpened(object sender, EventArgs e)
        {
            foreach (RadItem item in this.radRibbonBar1.RibbonBarElement.ApplicationButtonElement.DropDownMenu.Items)
            {
                RadMenuItem menuItem = item as RadMenuItem;
                if (menuItem!=null)
                {
                    menuItem.MinSize = new Size(item.Size.Width, 24);
                }
                
            }
        }

If ribbon group is collapsed and we open its drop-down panel and click on its dialog launcher then nothing happens. Observed in clean Word-inspired project (Font and Paragraph groups have launchers).

When a form's width is reduced enough then some groups in ribbon bar will become collapsed and in group's place a drop-down arrow is shown. When this arrow is clicked it will show properly its active state in all themes except three Metro themes. In Metro themes arrow's active state is such that only upper half of the control is visible. The issue is shown in current documentation for RadRibbonBar in the following image:

 

 

Problem similar to issue 1385801. When a group is collapsed (not the tab, but the group) then there is no way to scroll the list of a gallery element in this group. Issue can be seen in Word-inspired project with Styles gallery in Home tab. Reduce form's width so that Styles group is collapsed and then open the group in a new popup and try to scroll down the list of the Styles gallery.

Hello,

 

you will find in attached image the problem for File Tab button regarding its look in the editor and when running the application. How can I resolve this difference ?

 

Best regards